SSblack98

iTrader: (8)

I am wondering what a reasonable setup would be for one of the low comp 402s that are available virtually everywhere now. Would a T76 be ok especially for the street or would you have to run a 80 or bigger? I'm looking for a 402 turbo setup that makes at least 650rwhp on 93 pump gas. I have also seen 370ci turbo engines making great power, so would it be better to go with a smaller (less then 383ci) engine with a T76? I know a little about turbos but nothing like you guys on here so I'm having a hard time making a good decision as to what cube bottom end I should shoot for. I really don't want to exceed the size of a T76 for streetablility. Also, are T76 and 70mm turbos the same or are T76=76mm? Sorry for dumb questions. Thanks for any info...

Chad

98turbls1

iTrader: (17)

T76 is definitely bigger than a T70...It is in mm...If I were to go with a 402 I would probably go with a T88 because a T76 would probably be out of breath in the upper rpms if you decided to turn it up...What are your goals??

98turbls1

iTrader: (17)

You also may want to look at the AR of the turbo...that has to do with the spool time...If you get too small of one then it will spool quicker but not be good on the upper rpms..Too big and it will take longer to spool...Turbos are a definite give and take

RUSH

The 76 is still great for your set up. Spool time is decent and if you want better spool, go with a smaller housing. The 88 is really border for streetability, but hey, if you can drive on the street and deal with the craziness of the spool and all of a sudden boost, than its a god one as well. I have a "monster 91.5 on my GN, and I cant even tell you how crazy its going to be once its back in my hands from Conelys this month. Its definitly not a street driven turbo either, suppose to be uesed for pure drag, back halfed cars, but, I think I can deal with it. Its really your preference. The 76 once again is a very solid and very potent street/strip turbo. If your set up is wicked enough, those things can pull 800 rwhp on race gas, and little less on 93. Just make sure its all the vitals are being monitered, knock etc. Good luck

SSblack98

iTrader: (8)

Ok here is the deal. I am looking for 650rwhp on 93 octane and maybe 750-800rwhp on race gas but this will primarily stay a street car with maybe 3-4 trips to the track per year and probably 8-10k miles on the street. I have a heads/cam 346 in it now that I have been happy with but the drivability is only ok and I'm really about maxed out as far as stuff to increase power and not further hurt driveability. So...I have always wanted a turbo ls1 and I'm going in that direction but I can't figure out if I would best meet my goals by building the bottom end on the 346 thats in the car, or stroke the 346 to maybe 374 or 383, or just go for a low comp 402 shortblock. If 650 is realistic with the 346 I will just pull it out and forge it but if there is a good chance I willl not meet that goal I would like to up the cubes while I have the motor out.

Now for a turbo, if I need the size of a T88 for a 402 I think I will go smaller ci so I can use a more reasonably streetable turbo. What do you guys think about throwing a 3.9" crank in my current engine to get about 374ci and then going with the T76? Would I definitely be able to make 650 on pump gas? Has anyone done a 383 with a turbo? I was always under the inpression that you wanted a shorter stroke/quicker revving engine for a turbo application. That is why I was thinking about going with the 3.9" stroke even though the cranks are the same price.

Thanks for the input so far, everyone has been really helpful. I just don't want to spend money unnecessarily on a 402 if I would be better going smaller.

smokinHawk

iTrader: (48)

just make sure its a T6 flanged turbo.

SSblack98

iTrader: (8)

Are you refering to a 402 or a T76 on any 346 and greater engine? How critical is having a undersquare engine? In other words, I can build a 383 for around $2600-2800 including machine shop costs using my block and a 402 would be around $4k but would the oversquare 383 not be good for a turbo app? Should I just stick with stock ci? I hate to spend the money on forged internals and not up the size of anything.

YOUR03COBRA8ME

im going with a 402 and a t76 as well this should be more than enough to meet your standards

smokinHawk

iTrader: (48)

T6 im just refering to the turbo inlet size, if going bigger then 370 cubes id use a T6 instead of a T4.
if your only wanting 650RWHP you could do a stock stroke weather its a 4" bor or a 3.9, both should be able to produce the power, though the bigger the engine it will be easier to get on pump.
A gt42-76mm would probably be your gest choice, . though if you have a hard tije fitting one of those in your engine bay id just go with a PT76gts and definatly dont go bigger then a 370 cubes cause i think you can only get those in a t4 flange

Pro Stock John

iTrader: (34)

More cubes you run, more air you pump, the more backpressure you could have at the turbo.

There is no tried and true formula on the site. But if you run a 402ci and want to make 650rwhp or more, You will want at least a 76mm turbo, and up to a 88mm one. The Speed Inc. guys have gone a bunch of those Speed/TTi race kits, and I'm not sure what size turbo most of those guys have, but I'm guessing either 76 or 88mm turbos with T4 flanges. They make 750rwhp easily.

88 with a T6 flange is capable of making 1400hp or more. An 88 with a T4 flange will typically rated up to 1200hp.

If I would building a street car LS1 I would probably be looking at 80mm T4 flange stuff.

SSblack98

iTrader: (8)

My plan was to build the engine and then go with a Hi-Flo turbo kit and upgrade the turbo to the appropriate size based on what ci the engine ends up being. Since the cubes are fairly cheap to increase while rebuilding the engine anyway, I would rather do so if I will have a much better chance of meeting my goal. But I don't want to build a bigger engine and then choke it down with a turbo that is too small trying to keep it reasonable on the street. I don't know what turbo upgrades are available through Hi-Flo. I think the base kit is a 70mm which is obviously too small. I like their kit because of the placement of the turbo up top. Any opinions on going with their kit? I know a custom kit would be the best way to go but after I get the engine built and the fuel system upgraded, the turbo kit budget will probably be in the $5-6k range which from what I have seen puts custom kits out of the question. Thanks again for all the input!

SSblack98

iTrader: (8)

Thanks for the input John. I agree the 80mm seems like a good choice for a street/strip car. So you think I should not waste the money on stroking my 346 to 370-383ci and just go for the 402 and put a 80mm on it? My thought was that with a 402/9:1 comp and conservative 10-12psi on 93 octane I could easily see the 650rwhp I want to. And turn it up on race fuel for around 800rwhp.

2001-WS6

The Innovative 80mm on the TTi kit does move plenty of air for the street on a 400ci+ motor. We'll stretch its lungs out this year at the track and see how it does this spring.

Rick

Pro Stock John

iTrader: (34)

Rick does yours have a T4 flange?

2001-WS6

Your estimate is very reasonable for a 402/9:1 on 80mm TTi setup. My second trip to the track (422/9.2:1) in May last year put 16 passes down on MT 325/50/15 DRs with Sunoco 94 octane in the 10.09-10.36s range and 136-137mph on 11lbs of boost.

Tuning is the key and you need the suspension and driveline hardware to support it but it's very do able for your goals.

Rick

2001-WS6

Yep, its the stock TTi setup right now. No MM pipe updates yet.

Rick

Pro Stock John

iTrader: (34)

MM pipe?

My recollection is that a 76mm might do 1000hp, and the fastest example is Mike Murillo going high 8's. I don't know what size engine that is, but if it's small cubes it makes sense.

98Z28MASS

iTrader: (6)

You could do a forged 346 and hit 600+ rwhp, its just that your power curve will be a little bit more peaky than with a 383 or a 402, but it can be done. Id say check out the boosted list for the past 3 years and check out the setups that other people are running to see what fits your goals.

2001-WS6

David-MM did some rework on his pipe/flange to fit the new turbo last year when he upgraded from the Innovative 80 turbo. So I was referring to that as the MM pipe upgrade.

We'll make some more progress this year. It'll be more fun for the family school bus.

Rick

SSblack98

iTrader: (8)

Thanks to all for the input. I think I am going to save a little more $ and go with a 402 shortblock already assembled. It will put off the turbo kit a bit longer but I think it will be worth it in the end. Plus I would like to have a bit more grunt until I get the turbo so the 402 should do the trick even in low comp form. Does anyone have an opinion about what turbo kit would be the best, preferably one that is offered with a 80mm upgrade? The a/c is off the car now but I will likely be putting it back on and would like to be able to keep it but if it gets in the way of meeting my hp goals I would be willing to lose it. I like the turbo up top too so if the HiFlo is available w/80mm I will probably go that route. I really like the Speed Inc/Innovative package also but I probably won't have $8k to spend.